Medieval Warm Period Under Attack, Again

Once again the fear-mongering hoards of lay-climatologists are denouncing the importance of the Medieval Warm Period (MWP), or Medieval Climate Optimum as some refer to it. On the strength of a single new study, involving algal lipids from a lake in Svalbard, Norway, one pundit referred to the “so-called” Medieval Warm Period and impugned the significance of the Little Ice Age for good measure. Of course the writer, an “ecological journalist,” saw nothing wrong with using such a dismissive and pejorative term since it is IPCC promoted doctrine that today things are warmer than they have ever been since the onset of the Holocene. Yet literally hundreds of other studies have shown that the MWP was as warm or warmer than today and that is the real consensus among paleoclimatologists.

It is interesting how the mindless backers of conventional climate change doctrine—creatures of consensus all—are always quick to dismiss any new work that discredits or even slightly diminishes the received wisdom from the church of IPCC. Interesting because they are among the first to trumpet the publication of a single study that even marginally supports their position. Case in point is the publication of a new paper by William D’Andrea et al., published in the journal Geology. This paper, “Mild Little Ice Age and unprecedented recent warmth in an 1800 year lake sediment record from Svalbard,” was seized upon by Michael D. Lemonick, a longtime global warming cheerleader, as proof that the MWP really does not matter:

The so-called Medieval Warm Period (MWP), a 400-year span from about 950 to 1220 A.D. when the Vikings colonized Greenland, was relatively balmy by the standards of the past 2,000 years, leading some to argue that the global warming we’re now experiencing isn’t that big a deal. But a new report in the journal Geology argues that the MWP wasn’t all that warm after all — and certainly not as warm as the climate is today.

According to Lemonick's article, published on the pro-climate change website Climate Central and picked up by such scientifically inept “news” sources as the Huffington Post, the report is important because it reinforces the conclusion that humans are now putting their own “imprint” on the climate. But what does the report really say and mean? Here is a description of the work and major conclusions from the authors:

The Svalbard Archipelago occupies an important location for studying patterns and causes of Arctic climate variability; however, available paleoclimate records from Svalbard are of restricted use due to limitations of existing climate proxies. Here we present a sub-decadal- to multidecadal-scale record of summer temperature for the past 1800 yr from lake sediments of Kongressvatnet on West Spitsbergen, Svalbard, based on the first instrumental calibration of the alkenone paleothermometer. The age model for the High Arctic lake sediments is based on 210Pb, plutonium activity, and the first application of tephrochronology to lake sediments in this region. We find that the summer warmth of the past 50 yr recorded in both the instrumental and alkenone records was unmatched in West Spitsbergen in the course of the past 1800 yr, including during the Medieval Climate Anomaly, and that summers during the Little Ice Age (LIA) of the 18th and 19th centuries on Svalbard were not particularly cold, even though glaciers occupied their maximum Holocene extent.

So Lemonick 's report is accurate in claiming that, according to William D’Andrea and his co-authors, summer temperatures in the Svalbard Archipelago, a group of islands in the Arctic Ocean about 400 miles north of Norway, have been between 3.6°F and 4.5°F higher over the past 25 years, on average, than the summers the Vikings enjoyed during the MWP. But that is not the entire story here. Note that the author's also mention that Svalbard was not that cold during the Little Ice Age, a well documented cold period that followed the MWP. This is quite possibly a result of the Svalbard Archipelago's unique geographic location.

As can be seen from the map above, Svalbard is an archipelago in the Arctic, constituting the northernmost part of Norway. It is located about 400 miles north of mainland Europe, midway between mainland Norway and the North Pole. Its biggest claim to fame is that it is the single largest breeding ground for polar bears, who outnumber the area's human inhabitants during the spring and summer. The archipelago features an Arctic climate, although with significantly higher temperatures than other areas at the same latitude. This is due to its unique location and the moderating warm currents that flow around it from more southern waters. What is not usually mentioned is that the surrounding waters make this location different from others in the arctic region.

In short, this is one result from one lake in an atypical location, a problem that even Lemonick had to acknowledge. “One possible criticism of the study is that it’s based on just one location,” he states. “Maybe this lake, or this region, was significantly cooler during the MPW for some reason than the rest of the world.” Yet this qualification did not diminish the headline hype: “So-Called Medieval Warm Period Not So Warm After All.”

Shells from the 10th to 12th centuries (early MCA) were collected from well-stratified horizons, which accumulated in Viking shell and fish middens at Quoygrew on Westray in the archipelago of Orkney, Scotland. Their ages were constrained based on artifacts and radiocarbon dating of bone, charred cereal grain, and the shells used in this study. We used measured δ18OWATER values taken from nearby Rack Wick Bay (average 0.31 ± 0.17‰ VSMOW, n = 11) to estimate SST from δ18OSHELL values. The standard deviation of δ18OWATER values resulted in an error in SST estimates of ± 0.7 °C. The coldest winter months recorded in the shells averaged 6.0 ± 0.6 °C and the warmest summer months averaged 14.1 ± 0.7 °C. Winter and summer SST during the late 20th century (1961–1990) was 7.77 ± 0.40 °C and 12.42 ± 0.41 °C, respectively. Thus, during the 10th to 12th centuries winters were colder and summers were warmer by ~ 2 °C and seasonality was higher relative to the late 20th century. Without the benefit of seasonal resolution, SST averaged from shell time series would be weighted toward the fast-growing summer season, resulting in the conclusion that the early MCA was warmer than the late 20th century by ~ 1 °C.

Granted, this study was likewise from a different isolated location and used yet another proxy measurement. Where lies the truth? First one must remember that science is really in the best guess business, not the truth business. The controversy over the MWP has raged for half a century with many, many papers on both sides. According to one survey paper, the preponderance of studies came down on the side of “as warm or warmer than today” side. A welth of data is available from the Medieval Warm Period Project where there were at last count 765 different scientists from 453 research institutes listed that have worked on the medieval warm period. Of course, judging an issue based on the weight of paper on either side is probably no better than taking a vote, and science is not about taking votes.

So what if the MWP was not actually warmer than today's temperatures? Perhaps the Roman Warm Period (250 BC to 400 AD) was warmer, or the well known Holocene Climate Optimum (~7,000 to 3,000 BC). The HCO is called “optimum” because it is believed to have been measurably warmer than today's climate. Looking even further into the past, there are indications that other interglacials have been much warmer and longer than today’s Holocene interglacial. Yet for warmists the term unprecedented seemingly means “only things we choose to remember.” The war of claim and counter claim rages on in the media.

Viking Greenland was a happening place during the MWP.

This blog has reported on the MWP before (see “Medieval Warm Period Rediscovered”) and my readers know I place no stock in consensus science. All honest climate scientists will admit that the exact temperatures during the MWP are not accurately known and probably never will be. So why all the fuss every time a paper comes out either for or against a hotter MWP? It is because of the ridiculous claim by the IPCC and its followers that says temperatures today are hotter than they have ever been, or at least during this interglacial.

Having put so much emphasis on the “unprecedented” nature of current global warming, the proponents of anthropogenic global warming just cannot back down from the hottest ever claim. The argument is that if the Medieval Warm Period was hotter, then today's temperatures are not anything special and the whole global warming crisis is just so much hokum. This means that skeptics are constantly searching for proof that things were hotter and true believers desperate to discredit that proof. This, my friends, is not a scientific argument, it is a political one, and it would not be so viciously defended by global warming proponents if their scientific case was not so fundamentally weak itself.

Researchers, from the National University of Mexico and the Woods Hole Oceanographic Institution in the USA, writing in the journal Paleoceanography, point out that accurate low-latitude sea surface temperature records that predate the instrumental era (post-1850) are needed to put recent warming in the context of natural climate variability and to understand what they describe as the possible influence of anthropogenic climate change on this variability...

...The graph they produce is fascinating. It shows a decline in sea surface temperature from 1773 to 1860, then a peak at 1880 which then declines to 1910. The year 1910 is a significant one for those studying rises in sea level as it is from 1910 that the gradient of recent sea level rise changes and persists that that rate of increase to the present day.

A new paper, looking back at the climate of the past two thousand years, published in the journal “Climate of the Past,” will either cause something of a stir, or provide confirmation of what some regard as having already emerged from the peer-reviewed scientific literature. The title of the paper is, “The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability,” by B Christiansen of the Danish Meteorological Institute and F C Ljungqvist of Stockholm University. More at